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CN-117561213-B - Dual pressure system for producing nitric acid and method of operating the same

CN117561213BCN 117561213 BCN117561213 BCN 117561213BCN-117561213-B

Abstract

The present disclosure discloses a production plant for producing nitric acid at reduced power, the system being derived from a state-of-the-art dual pressure nitric acid plant, characterized in that the system further comprises first means for splitting the off-gas stream into a first off-gas stream and a second off-gas stream in fluid communication with compressed air and oxygen enriched gas, and/or means for splitting the off-gas stream into a third off-gas stream and a fourth off-gas stream in fluid communication with compressed air and oxygen enriched gas. The production facility of the present disclosure allows for power reduction by an air compressor. The present disclosure further relates to a method for operating the system, the use of the system of the present disclosure for performing the method of the present disclosure, and a method for retrofitting a state-of-the-art dual pressure nitric acid plant to the system of the present disclosure.

Inventors

  • BENT VIGELAND
  • Halvo Erin
  • Krzyshtov Baonaoshiyak
  • ANDRE DESMET
  • Peter Fouconier

Assignees

  • 亚拉国际有限公司

Dates

Publication Date
20260505
Application Date
20220825
Priority Date
20210825

Claims (20)

  1. 1. A production facility for producing nitric acid with reduced power consumption and reduced emissions, comprising: An air compressor providing compressed air; a supply of a first oxygen-enriched gas, the mixing of the first oxygen-enriched gas with compressed air providing a portion of the first oxygen-containing gas; mixing means for mixing the first oxygen-containing gas with an ammonia gas stream to produce an ammonia/oxygen-containing gas mixture; An ammonia converter configured to operate at a pressure equal to or higher than P1 and lower than P2 for oxidizing ammonia in the ammonia/oxygen-containing gas mixture to produce a NOx gas/steam mixture comprising water and nitrogen oxides; Means for adjusting the ammonia concentration and/or the oxygen concentration in the ammonia converter, for maintaining the oxygen to ammonia molar ratio inside the ammonia converter at a ratio of at least 1.2; A first gas cooler/condenser downstream of the ammonia converter to produce an aqueous dilute nitric acid mixture and a gaseous NOx stream; A NOx gas compressor for compressing the gaseous NOx stream to produce a compressed NO x gas stream at a pressure P2; An absorber for absorbing the NO x gas from the compressed NO x gas stream in water to produce a crude nitric acid stream containing residual NO x gas and a tail gas comprising NO x gas, comprising an absorber tail gas outlet for evacuating the tail gas; A heat exchange system upstream of the gas cooler/condenser for heating an exhaust stream with heat from the NO x gas/steam mixture of the ammonia converter; a second gas cooler/condenser for separating and condensing vapor from the compressed NO x gas stream prior to providing the stream to the absorber column; A second oxygen-containing gas having: a) A pressure equal to or higher than P1 and not exceeding P2 for supplying oxygen downstream of the ammonia converter and upstream of the NO x gas compressor, or B) A pressure above P2 for supplying oxygen to the compressed NO x gas stream; Means for controlling the flow of said second oxygen-containing gas such that the tail gas stream contains at least 0.5% oxygen by volume, and A first pressure relief device downstream of the heat exchange system for expanding the exhaust gas stream to produce a first expanded exhaust gas having a pressure equal to or higher than P1 and lower than P2, wherein the first pressure relief device is configured to at least partially power the NO x gas compressor and/or the air compressor; characterized in that the production device further comprises: first and/or second means for diverting a gas flow, wherein (I) The first splitting means is means for splitting the exhaust gas stream into a first exhaust gas stream and a second exhaust gas stream, wherein the first exhaust gas stream has a pressure equal to or greater than P1 and no greater than P2 and is in fluid communication with the first oxygen-enriched gas and compressed air, and wherein a mixture of compressed air, the first oxygen-enriched gas, and the first exhaust gas stream provides the first oxygen-containing gas, and (Ii) The second flow splitting means is means for splitting the off-gas stream into a third off-gas stream and a fourth off-gas stream, wherein the third off-gas stream has a pressure equal to or higher than P1 and not exceeding P2 and is in fluid communication with compressed air and the first oxygen-enriched gas, and wherein the mixing of the third off-gas, compressed air and the first oxygen-enriched gas provides the second oxygen-containing gas, and wherein the second oxygen-containing gas is supplied downstream of the ammonia converter and upstream of the NO x gas compressor; Or alternatively The second flow splitting device is a device for splitting the off-gas flow into a third off-gas flow and a fourth gas flow, and wherein the third off-gas flow is in fluid communication with compressed air and the first oxygen-enriched gas, and wherein the mixing of the third off-gas, compressed air and the first oxygen-enriched gas and the pressurization of the mixed third off-gas, compressed air and the first oxygen-enriched gas in a pressurization device provides the second oxygen-containing gas at a pressure higher than P2, and wherein the second oxygen-containing gas is supplied downstream of the NO x gas compressor and upstream of the absorber.
  2. 2. The production plant of claim 1, wherein the production plant further comprises means for controlling the flow of the first and/or third tail gas streams.
  3. 3. The production apparatus of any one of claims 1 to 2, wherein the production apparatus further comprises one or more of: A steam turbine, wherein the steam turbine is configured to at least partially power the NO x gas compressor and/or the air compressor; a heat exchanger for exchanging heat between the first expanded tail gas and a tail gas stream that is cooler than the first expanded tail gas, wherein the first expanded tail gas exits the heat exchanger at a temperature of less than 300 ℃, and wherein: -said first expanded tail gas downstream of said heat exchanger is in direct fluid communication with said first dividing means, and/or -Said tail gas stream cooler than said first expanded tail gas is split into a third tail gas stream and a fourth tail gas stream; A NO-removing x processing unit, and Second pressure relief means for expanding the second tail gas stream to atmospheric pressure to produce a second expanded tail gas.
  4. 4. The production facility of any one of claims 1 to 2, further comprising a bleach for bleaching the crude nitric acid stream containing residual NO x gas to provide a bleached nitric acid stream, the bleach having an inlet in fluid communication with a high pressure water electrolysis cell supplying an oxygen-enriched bleaching gas and an exhaust outlet in fluid communication with any gas stream downstream of the ammonia converter and upstream of the NO x gas compressor if the bleach is operated at a pressure equal to or higher than P1 and not exceeding P2, or with any stream downstream of the NO x gas compressor and upstream of the absorber tower if the bleach is operated at a pressure higher than P2, such that the supply of the second oxygen-containing gas is at least partially from the exhaust gas.
  5. 5. The production facility of any one of claims 1 to 2, further comprising a second oxygen-enriched gas stream in direct fluid communication with any of the tail gas streams.
  6. 6. The production plant according to any one of claims 1 to 2, wherein the first oxygen-enriched gas and the second oxygen-containing gas are at least partially provided by a high pressure water electrolyzer.
  7. 7. The production facility of claim 5, wherein the second oxygen-enriched gas of the second oxygen-enriched gas stream is at least partially provided by a high pressure water electrolyzer.
  8. 8. The production facility of claim 4 wherein the oxygen-enriched bleaching gas and the off-gas are provided at least in part by a high pressure water electrolyzer.
  9. 9. The production plant according to claim 1, wherein the means for adjusting the ammonia concentration and/or oxygen concentration in the ammonia converter is means for controlling the flow of the first oxygen-enriched gas in the oxygen-containing gas and/or means for controlling the flow of the ammonia gas stream.
  10. 10. The production facility of claim 5, wherein the second oxygen-enriched gas stream is a pressurized oxygen-enriched gas stream in direct fluid communication with any tail gas stream upstream of the first pressure relief device.
  11. 11. A method of producing nitric acid with reduced power consumption and reduced emissions in a production plant according to any of claims 1 to 10, comprising the steps of: a) Compressing air in the air compressor to thereby provide compressed air; b) Supplying the compressed air obtained in step a) to the mixing device; c) Supplying the ammonia gas stream to the mixing device, thereby producing the ammonia/oxygen-containing gas mixture; d) Oxidizing ammonia in the ammonia/oxygen-containing gas mixture in the ammonia converter at a pressure equal to or higher than P1 and lower than P2, thereby producing the gaseous NO x gas/steam mixture comprising water and nitrogen oxide; e) Cooling the NO x gas in the gaseous NO x gas/vapor mixture in the heat exchange system and the gas/cooler condenser, thereby producing an aqueous dilute nitric acid mixture and the gaseous NO x stream; f) Compressing the gaseous NO x stream in the NO x gas compressor, thereby providing a pressurized NO x compressed gas stream having a pressure P2; g) Absorbing the pressurized gaseous NO x stream in the absorber column, thereby providing the crude nitric acid stream containing residual NO x gas and the tail gas comprising NO x gas; h) Heating the tail gas in the heat exchange system with heat from the NO x gas/steam mixture of the ammonia converter; i) Cooling the compressed NO x gas stream in an additional gas cooler/condenser, and J) Expanding at least a portion of the tail gas obtained in step h) in the first pressure relief device, thereby providing the first expanded tail gas; characterized in that the method further comprises the steps of: k) Splitting the tail gas stream into a first tail gas stream and a second tail gas stream with a first splitting device and/or splitting the tail gas stream into a third tail gas stream and a fourth tail gas stream with a second splitting device; l) mixing the first offgas stream with the first oxygen-enriched gas and compressed air, thereby providing the first oxygen-containing gas, and/or mixing the third offgas stream with compressed air and the first oxygen-enriched gas, thereby providing the second oxygen-containing gas; m) adjusting the flow of the first oxygen-enriched gas or the flow of the ammonia gas stream mixed in step l) to maintain the oxygen to ammonia molar ratio inside the ammonia converter at a ratio of at least 1.2; n) supplying the first oxygen-containing gas to a mixing unit; o) adjusting the flow of the second oxygen-containing gas such that the tail gas stream contains at least 0.5% oxygen by volume, and P) supplying the second oxygen-containing gas downstream of the ammonia converter and upstream of the NO x gas compressor at a pressure equal to or higher than P1 and not exceeding P2, or downstream of the NO x gas compressor and upstream of the absorber at a pressure higher than P2.
  12. 12. The method of claim 11, further comprising the step of: q) adjusting the flow of the first and/or the third tail gas stream.
  13. 13. The process according to any one of claims 11 to 12, wherein in step i) the first tail gas stream is mixed, and wherein in step k) the first expanded tail gas is split, and wherein the process further comprises the steps of: r) heating in the heat exchanger the tail gas cooler than the first expanded tail gas together with the first expanded tail gas obtained in step j) so that the tail gas to be mixed in step l) reaches a temperature below 300 ℃; s) treating the tail gas stream heated in step r) in a NO-removal x treatment unit; t) expanding the second tail gas stream in a second pressure relief device to provide a second expanded tail gas, and U) recovering at least a portion of the heat energy generated in the ammonia converter in the steam turbine.
  14. 14. The process according to any one of claims 11 to 12, wherein the third offgas stream is mixed in step i), and wherein the offgas obtained in step g) is split into a third offgas stream and a fourth offgas stream in step k).
  15. 15. The method according to any one of claims 11 to 12, further comprising the step of: v) bleaching said crude nitric acid stream containing residual NO x gas obtained in step g) in a bleach, thereby producing a bleached nitric acid stream.
  16. 16. The method according to any one of claims 11 to 12, further comprising the step of: w) supplying a second oxygen-enriched gas stream to the tail gas stream.
  17. 17. The method according to any one of claims 11 to 12, further comprising the step of: x) operating the high pressure water electrolyzer to produce pressurized oxygen, and Y) providing at least a portion of the first oxygen-enriched gas, the second oxygen-containing gas, the oxygen-enriched bleaching gas and the oxygen-enriched exhaust gas from the oxygen produced by the water electrolysis cell in step x).
  18. 18. The method of claim 11, wherein in step h) the tail gas is heated in the heat exchange system with heat from the NO x gas/steam mixture of the ammonia converter to a temperature in the range of 150 ℃ to 650 ℃.
  19. 19. The method according to claim 11, wherein in step i) the compressed NO x gas stream is cooled in an additional gas cooler/condenser, thereby providing the compressed NO x gas stream having a temperature in the range of 20 ℃ to 60 ℃.
  20. 20. The method of claim 16, wherein the second oxygen-enriched gas stream is supplied to the tail gas stream as a pressurized oxygen-enriched gas stream.

Description

Dual pressure system for producing nitric acid and method of operating the same Technical Field The present disclosure relates to the field of nitric acid production in dual pressure equipment. Introduction to the invention Pure nitric acid is a transparent colorless liquid with strong odor. Nitric acid is produced in large quantities mainly by catalytic oxidation of ammonia (Ostwald process). Ammonia is converted to nitric acid in several stages. Ammonia is first oxidized in an ammonia burner on a platinum wire mesh (commonly referred to as an ammonia converter) or cobalt balls, producing nitrogen oxides (also referred to as Nitric Oxide (NO) in this disclosure) and water: 4NH3(g)+5O2(g)→4NO(g)+6H2O(g) (1) the reaction product nitrogen oxide from (1) is then oxidized after cooling to nitrogen dioxide (NO 2) and further to dinitrogen tetroxide N 2O4 (g) in an oxidation zone: 2NO(g)+O2(g)→2NO2(g) (2) 2NO2(g)→N2O4(g) (3) The cooling of the nitrogen oxide gas is accomplished by first recovering the heat of conversion of ammonia to nitrogen oxide using a waste heat recovery system, then by using a chiller condenser in which condensed nitric acid is separated from the nitrogen oxide, nitrogen dioxide, and dinitrogen tetroxide and nitric acid gases, collectively referred to as NOx gas, and finally by heating the tail gas released at the outlet of an absorber column in which NO x gas is absorbed. Nitrogen dioxide and dinitrogen tetroxide are converted to nitric acid and nitric oxide by absorption in water, followed by compression via a NO x gas compressor: 3NO2(g)+H2O(l)→2HNO3(aq)+NO(g) (4) 3N2O4(g)+2H2O(l)→4HNO3(aq)+2NO(g) (5) Up to 68% of weak nitric acid (azeotrope) is obtained. Through the rectification process, the concentration of nitric acid can be increased by 99% of concentrated nitric acid. The total reaction is given by: NH3+2O2→HNO3+H2O (6) The main process units in the nitric acid production plant include an ammonia converter (converting ammonia to nitrogen oxide over a suitable catalyst using oxygen), an oxidation zone (converting nitrogen oxide to nitrogen dioxide and dinitrogen tetroxide), an absorber unit (for absorbing NO x gas into water) and a bleach unit (removing unreacted dissolved gases, in particular dissolved gases containing NO x and gases, from the aqueous nitric acid solution, giving it a typical brown color). The production process of nitric acid can be classified into single-pressure (single-pressure) and double-pressure (partial pressure) processes. In a dual pressure process, the absorber unit is operated at a higher operating pressure than the ammonia converter. Modern dual pressure processes are characterized by low pressure ammonia converters typically operating at 2 bar to 6 bar and high pressure absorber units operating at 9 bar to 16 bar. The dual pressure process requires an air compressor to feed low pressure air (which contains about 21% oxygen by volume) to the converter and an NO x gas compressor to feed high pressure NO x gas to the absorber unit. The operating pressure of the air compressor is 2bar to 6 bar inclusive and the operating pressure of the NO x gas compressor is 9 bar to 16 bar inclusive. The driving force for the air compressor is typically derived from an exhaust gas turbine and a steam turbine or a power source (such as an electric motor). Accordingly, the compressor train of a dual pressure nitric acid production plant typically includes an air compressor, a NO x gas compressor, an exhaust gas turbine, and a steam turbine or power source (such as an electric motor). In more detail, referring to fig. 1, the dual press apparatus and process according to the related art operates in the following manner. The gaseous ammonia 32, optionally preheated in a preheater unit (not shown), is mixed in a mixing device 35 with compressed air 34 pressurized to low pressure using an air compressor 36 and the resulting ammonia/oxygen enriched air mixture 14 is fed to an ammonia converter 37 operating at low pressure, wherein the ammonia is oxidized over a suitable catalyst, obtaining an LP NO x gas/steam mixture 15 comprising water and Nitrogen Oxide (NO). The heat of the mixture exiting the ammonia converter is recovered, after which the NO x gas/stream mixture is subsequently cooled in a gas cooler/condenser 38 to a temperature at which water is condensed, and the aqueous dilute nitric acid mixture 17 is separated from the gaseous NO x stream 22. Gaseous NO x stream 22 is sent to NO x gas compressor 40 where its pressure is raised from low pressure to high pressure, approximately equal to the operating pressure of absorber unit 41. The aqueous dilute nitric acid mixture 17 is sent to an absorber unit 41, commonly referred to as an absorber column. The pressurized NO x gas stream 24 is further oxidized to further convert NO to NO 2 and N 2O4, cooled in an additional gas cooler/condenser 39, and then directed to the absorber column 41. Within absorber column 41, pre